The paper describes our participation in Monolingual tasks at CLEF 2007. We submitted results for the following languages: Hungarian, Bulgarian and Czech. We focused on studying different query expansion techniques: Probabilistic Relevance Feedback (PRF) and Mutual Information Relevance Feedback (MI-RF) to improve retrieval performance. After an analysis of our experiments and of the official results at CLEF 2007, we achieved considerably improved scores by using query expansion techniques for different languages (Hungarian, Bulgarian and Czech). Categories and Subject Descriptors H.3 [Information Storage and Retrieval]: H.3.3 Information Search and Retrieval General Terms Experimentation, Performance, Query Expansion Keywords Information Retrieval